 /*******************************************************************************
  * Copyright (c) 2000, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.actions;

 import org.eclipse.jface.action.Action;
 import org.eclipse.jface.viewers.ISelection;
 import org.eclipse.jface.viewers.ISelectionChangedListener;
 import org.eclipse.jface.viewers.ISelectionProvider;
 import org.eclipse.jface.viewers.IStructuredSelection;
 import org.eclipse.jface.viewers.SelectionChangedEvent;
 import org.eclipse.jface.viewers.StructuredSelection;

 /**
  * The abstract superclass for actions that listen to selection changes
  * from a particular selection provider. This implementation splits the current
  * selection along structured/unstructured lines, providing a convenient place
  * to monitor selection changes that require adjusting action state.
  * <p>
  * Subclasses must implement the following <code>IAction</code> method:
  * <ul>
  * <li><code>run</code> - to do the action's work</li>
  * </ul>
  * </p>
  * <p>
  * Subclasses may reimplement either of the following methods:
  * <ul>
  * <li><code>selectionChanged(IStructuredSelection)</code></li>
  * <li><code>selectionChanged(ISelection)</code></li>
  * </ul>
  * </p>
  */
 public abstract class SelectionProviderAction extends Action implements
         ISelectionChangedListener {

     /**
      * The selection provider that is the target of this action.
      */
     private ISelectionProvider provider;

     /**
      * Creates a new action with the given text that monitors selection changes
      * within the given selection provider.
      * The resulting action is added as a listener on the selection provider.
      *
      * @param provider the selection provider that will provide selection notification
      * @param text the string used as the text for the action,
      * or <code>null</code> if there is no text
      */
     protected SelectionProviderAction(ISelectionProvider provider, String text) {
         super(text);
         this.provider = provider;
         provider.addSelectionChangedListener(this);
     }

     /**
      * Disposes this action by removing it as a listener from the selection provider.
      * This must be called by the creator of the action when the action is no longer needed.
      */
     public void dispose() {
         provider.removeSelectionChangedListener(this);
     }

     /**
      * Returns the current selection in the selection provider.
      *
      * @return the current selection in the selection provider
      */
     public ISelection getSelection() {
         return provider.getSelection();
     }

     /**
      * Returns the selection provider that is the target of this action.
      *
      * @return the target selection provider of this action
      */
     public ISelectionProvider getSelectionProvider() {
         return provider;
     }

     /**
      * Returns the current structured selection in the selection provider, or an
      * empty selection if nothing is selected or if selection does not include
      * objects (for example, raw text).
      *
      * @return the current structured selection in the selection provider
      */
     public IStructuredSelection getStructuredSelection() {
         ISelection selection = provider.getSelection();
         if (selection instanceof IStructuredSelection) {
             return (IStructuredSelection) selection;
         } else {
             return new StructuredSelection();
         }
     }

     /**
      * Notifies this action that the given (non-structured) selection has changed
      * in the selection provider.
      * <p>
      * The <code>SelectionProviderAction</code> implementation of this method
      * does nothing. Subclasses may reimplement to react to this selection change.
      * </p>
      *
      * @param selection the new selection
      */
     public void selectionChanged(ISelection selection) {
     }

     /**
      * Notifies this action that the given structured selection has changed
      * in the selection provider.
      * <p>
      * The <code>SelectionProviderAction</code> implementation of this method
      * does nothing. Subclasses may reimplement to react to this selection change.
      * </p>
      *
      * @param selection the new selection
      */
     public void selectionChanged(IStructuredSelection selection) {
         // Hook in subclass.
 }

     /**
      * The <code>SelectionProviderAction</code> implementation of this
      * <code>ISelectionChangedListener</code> method calls
      * <code>selectionChanged(IStructuredSelection)</code> if the selection is
      * a structured selection but <code>selectionChanged(ISelection)</code> if it is
      * not. Subclasses should override either of those methods method to react to
      * selection changes.
      */
     public final void selectionChanged(SelectionChangedEvent event) {
         ISelection selection = event.getSelection();
         if (selection instanceof IStructuredSelection) {
             selectionChanged((IStructuredSelection) selection);
         } else {
             selectionChanged(selection);
         }
     }
 }

